Motor vehicles with internal combustion engines are sometimes equipped with an exhaust gas cooler or element in the exhaust system of the vehicle to permit cooling and/or recirculation of exhaust gas under certain operating conditions. The exhaust element has an inlet for receiving exhaust gas from the engine and an outlet for the exhaust gas to be recirculated back to the engine air intake or to other components in the exhaust line. Typically, the exhaust element includes an exhaust pipe extending between the inlet and outlet of the exhaust element, and a heat exchanger mounted generally in parallel with the exhaust pipe between the inlet and outlet of the exhaust element. Regulating or flow diversion means in communication with the inlet or outlet of the exhaust element directs the flow of the exhaust gas through either the exhaust pipe or through the heat exchanger to the outlet. When the exhaust gas is directed through the heat exchanger, the exhaust gas is cooled and the heat is transferred usually to the engine coolant. In addition to cooling the exhaust gas, this type of heat transfer is advantageous under cold conditions as it allows the cooling system in the vehicle to quickly reach optimal operating temperature, and the heated coolant can be used to warm up other fluids or areas of the vehicle. The exhaust element can be formed as either an “internal bypass” system wherein the heat exchanger and the bypass are enclosed in a common housing, or as an “external bypass” system wherein the heat exchanger and bypass are separate to each other with no common housing.
U.S. Pat. No. 6,141,961 to Rinckel discloses an exhaust element that includes a main exhaust pipe and a bypass. In this embodiment, the bypass is comprised of a heat exchanger mounted in parallel with and external to the main exhaust pipe. The main pipe is formed of two separate tubular sections that are joined by bellows to provide for some expansion of the main pipe. Moveable means for shutting off the main pipe and for regulating the cross-sectional area provided for the gases to pass through the bypass are arranged in the inlet end of the exhaust element. The moveable means are housed within a diverging adapter having a first end for coupling to the exhaust gas feed or inlet and a second end for coupling with the inlet of the main exhaust pipe and the inlet of the bypass. In order to accommodate the separate ends of the main exhaust pipe and the heat exchanger or bypass portion, the adapter includes a central strut member that effectively divides the second end of the adapter into two separate openings—one for receiving the inlet end of the main pipe and one for receiving the inlet end of the bypass. The cross-section of the strut member is generally in the form of a “hair-pin”, which allows the main pipe and the bypass to essentially be clamped together in their parallel relationship when the adapter is fitted on the ends thereof. A converging adapter is positioned at the outlet ends of the main pipe and the bypass for directing the flow of the exhaust gas to atmosphere.
The overall structure of Rinckel's exhaust element is somewhat complex in that the main exhaust pipe and bypass are held together by means of adapters with quite complex structures. More specifically, as mentioned above, the diverging adapter is formed with a complex hair-pin strut member that must be positioned on the ends of the main pipe and bypass before the exhaust element can be joined together, most likely by brazing. The overall assembly of the components is quite cumbersome, and it is difficult to achieve a proper seal or joint between the ends of the main pipe and bypass and the hair-pin strut member, which may affect the overall performance of the exhaust element and may increase the likelihood of failure.
International published application WO 2005/111385, in the name of Behr GmbH & Co. KG, discloses a heat exchanger for internal combustion engines having a first elongate flow channel for the passage of exhaust gas from the engine and a second flow channel or bypass arranged adjacent to the first flow channel, also for the passage of exhaust gases. The first and second flow channels are housed within a common housing and end caps or brackets, which fit into the ends of the housing, hold the first and second flow passages in place therein. The heat exchanger, therefore, can be classified as an internal bypass system. A medium such as a coolant is provided by means of a pipe in communication with the housing for heat exchange between the exhaust gas in the first flow channel and the medium. A valve channel with an adjustable valve element communicates with the inlet ends of the first and second flow channels for regulating or adjusting the amount of exhaust gas flowing through either the first or second flow channels. With an internal bypass arrangement, it is difficult to insulate the second or bypass channel from the first flow channel so that heat exchange between the two does not occur as both of the channels are usually in contact with the medium or coolant.